1. Field of the Invention
The present invention relates to a control system of a wind power generator, a wind farm, and a method for controlling the wind power generator.
2. Description of Related Art
Recently, a power generation device interconnected to a system is required to contribute to prevention of fluctuation in frequency (PFR: Primary Frequency Response) in a power system within a predetermined time (such as 30 seconds) after disturbance is generated in the power system (hereinafter, referred to as the “frequency response control”).
The frequency response control includes responses to an increase in frequency and a decrease in frequency of the power system. The increase in frequency of the power system is managed by limiting a power generation output of the wind power generator, and the decrease in frequency of the power system is managed by increasing the power generation output of the wind power generator.
A method for increasing the power generation output of the wind power generator includes a method to temporarily increase the power generation output of the wind power generator by converting inertial energy (referred to as inertia occasionally) possessed by a rotor of the wind power generator (hereinafter, referred to as the “inertial control”), and a method to supply power from an additional component such as a secondary battery, to the power system.
However, the above methods have the following problems.
As for the inertia control, since the inertial energy of the rotor is lost, a rotation speed of the rotor decreases and a relationship between the rotation speed and wind speed drops out of optimal control, so that while the frequency of the power system is decreasing, a power generation amount (provided by multiplying a power generation output by time) is reduced as compared with that in normal optimal control. Therefore, although a peak of the frequency decrease of the power system can be reduced by performing the inertia control, the problem is that the power generation output of the wind power generator is low as compared with an optimal output, which causes an increase in frequency decreasing time of the power system. Further, as for the power supply from the additional component, the problem is that cost increases because the additional component is provided.
In addition, other than the above two methods, as shown in US2010/0127495A1, there is a method to generate power while previously limiting the power generation output on an optimal (maximum) output of the wind power generator with respect to wind speed, and increase the power generation output of the wind power generator to the optimal output at the time of a decrease in frequency of the power system (hereinafter, referred to as the “deload operation”).
Thus, as for the frequency decrease in the power system, it is considered effective to operate the wind power generator in the deload operation and increase the power generation output of the wind power generator to the optimal output at the time of a frequency decrease because it is not necessary to provide the additional component, and power can be stably supplied to the power system in which the frequency decreases. However, the deload operation has the problem that a yearly power generation amount decreases in the wind power generator.